Windshield wiper drive mechanisms generally comprise a motor connected to a reciprocating mechanism which converts the rotary motion of the motor into a reciprocating motion of an output shaft. The output shaft may itself comprise the spindle of a wiper arm, or it may drive the wiper arm or arms via a suitable linkage. The reciprocating mechanism is designed to rotate the output shaft to and fro through an angle of rotation corresponding to the angular sweep of the wiper blades, which can vary from approximately 90.degree. to as much as 180.degree. depending on the design of the vehicle.
Wiper blades and their associated drive mechanisms have significant inertia and the reversal of movement of the output shaft at the limits of its reciprocating movement causes substantial shocks in the drive mechanism which may be noticeable to the vehicle occupants and which can result in rapid wear and even failure of the mechanism during extensive use. To overcome this problem, means have been proposed to brake the output shaft at least towards the limits of its reciprocating movement. This takes up the free play in the mechanism at this point and results in a cushioned reversal of movement of the wiper blades.
Various mechanisms have been proposed for achieving this. In one arrangement, a key on the output shaft drives a threaded collar which winds and unwinds during reciprocation of the shaft to move the collar to and fro along the shaft. The ends of the collar engage resilient washers which apply an axial load to the shaft, thereby damping movement of the shaft at the ends of its reciprocating motion. In another prior arrangement for limiting the sweeping angle of the windscreen wipers, the brake comprises a part-pinion having teeth which engage with stops formed on the end of a circular wire spring. These known arrangements are relatively complicated and significantly add to the cost of the drive mechanism.
It is an object of the present invention to provide an improved windshield wiper drive mechanism having damping means for braking the to and fro movement of the output shaft at least towards the limits of it reciprocating movement.
It is a further object of the present invention to provide such a mechanism in a simple and inexpensive form.